Download - L01 Ecosystems-what are they
Ecosystems – what are they ?
(Refer to Essentials of Ecology,G. Tyler Miller)
Ecosystems Levels of organization
Individual/OrganismPopulationCommunityEcosystemBiosphere
an Ecosystem consists of all of the organisms living in a community (or communities) together with the abiotic factors with which they interact
Rocky Shore community – an example• the mix of barnacles, algal mats, herbivorous snails
on rocks etc.• the physical environment (dessication, temp, wave
action) leads to a vertical zonation pattern• predation and competition influence distribution
eg. snails grazing algal spores, predatory snails eating herbivores
• disturbance opens spaces, allows establishment of new species
• different communities result in different locationsRocky Shore
community
Structure of a community is usually the result of many interactions
results from:
– many competitive interactions– complex mutualisms– predators increasing and decreasing– variety of disturbances through time– environmental fluctuations and more!
Biomes – ecosystems & communities on a global scale (Miller Ch 4 Fig 4.8)
• vegetation structure in different parts of the world is similar in similar environments - even though species are different
• biomes are communities with similar structure
Biosphere (ecosphere) - the biosphere (i.e. all ecosystems on earth) is an additional level of organization
• Existence of life depends upon– an energy source (the sun)– oxygen, carbon, nitrogen and other elements,
all of which are part of worldwide geological and chemical cycles
• All ecosystems on Earth are linked via global biogeochemical cycles.
• an ecosystem is all of the organisms living in a community (or communities) together with their abiotic factors
Ecosystem functionthrough
Energy flow Cycling of materials
• A systems approach attempts to understand– the way energy is passed through the system– how nutrients are cycled
• Individual organisms or species can be considered in terms of the function they perform
What does biodiversity actually do ?
biological diversity allows the different ecosystem functions to be carried out
the primary ecosystem functions are to
• Capture• Store• Transfer
Energy Carbon dioxide Nutrients Water
ECOSYSTEMS
ecosystems are a network ofinteractions, beginning withthe PRIMARY PRODUCERS(the PLANTS) andconnecting to herbivores,carnivores, parasites,decomposers
...energy, nutrients & waterare cycled through thenetwork by these differentgroups
Miller Ch 4 Fig 4.6
Flow of energy and materials through an ecosystem
Systems approach to ecosystem function
Essential characteristics of ecosystems
1. Energy flow
Energy flows in a unidirectional way (it does not cycle!) fig 4.13 Miller Ch 4
This requires a continuous input of energy into an ecosystem
Energy source autotrophs heterotrophs
Essential characteristics of ecosystems
1. Energy flow
• Autotrophs (e.g. plants, algae)
organisms capable of synthesizing all their required organic molecules from simple organic substances and an energy source
Essential characteristics of ecosystems
1. Energy flow• Heterotrophs (e.g. animals) organisms that cannot
synthesize complex organic compounds and must feed on organic material formed by other organisms to obtain energy and necessary molecular building blocks for metabolism and growth
Essential characteristics of ecosystems2. Cycling of materials
• Materials (e.g. carbon, nitrogen, phosphorus) are cycled from the abiotic environment, through living organisms, and back to the abiotic environment
• This results from metabolic activities of plants and animals, and organisms such as bacteria and fungi that break down organic matter
Energy in ecosystems• All organisms require energy
– maintenance, growth, reproduction, (and movement)
• The energy driving the biosphere (and all ecosystems) is solar radiation, captured via photosynthesis by autotrophs
• about 1% of visible light converted to chemical energy• about 120 billion tonnes of new organic material produced
each year• about 99% of all organic matter in the biosphere is autotrophs
(i.e. mostly plants)
Sunlight - the source of energy for the biosphere
Miller Ch 4 Fig 4.14
Photosynthesis
Photosynthesis
6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6H2O
Respiration
Energy (from photosynthesis) is released and used by the organism when the complex molecules are subsequently broken down during metabolism
(+ solar energy)
Productivity in ecosystems(Refer to David T. Krohne ;Pg 358-366)
Primary productivity - the rate at which solar radiation is converted into chemical energy by autotrophs (plants) (amount of material or energy per unit time, e.g. g/m2/yr)
Secondary productivity - the rate at which heterotrophs (animals) convert the chemical energy of their food into new tissue
Productivity in ecosystems• However, not all of the energy is converted into
new living tissues– respiration (metabolism) accounts for a large part
• Gross primary productivity - energy fixed in photosynthesis per unit time
• Nett primary productivity - energy fixed in photosynthesis minus energy used in respiration (that is, it is the amount available for harvest at next level)
Productivity in ecosystems
A measure of nett primary productivity is the change in biomass per unit time(but be aware of what may have been lost)
Biomass - the weight of living tissue per unit area (e.g. kg/ha)
What limits primary productivity?
(The factors that limit rate of photosynthesis limit production)
• light• water• temperature• nutrients (N, P, trace elements)
• all are essential - the resource in shortest supply will be the one limiting biomass production
Which are the most productive ecosystems on Earth?
Which are the most productive ecosystems?
Ecosystem Nett primary World primary production production (g/m2/yr) (billion t/yr)
Tropical rain forest 2200 37.4Woodland/shrubland 700 6.0Temperate grassland 600 5.4Desert and scrub 90 1.6Swamp and marsh 2000 4.0Open ocean 125 41.5Upwelling ocean zones 500 0.2Algal beds and reefs 2500 1.6
Productivity through time• Primary productivity will vary seasonally depending
on environmental conditions - ‘growing season’ in agriculture
- tropical vs temperate forests
• Productivity may change with the age of an ecosystem (regenerating vs older)
Young ecosystems - often a greater proportion of young actively growing tissue